Alloy



United States Patent 3,282,690 ALLOY Eugene J. Delgrosso, Wallingford, and John J. Kaminsky,

Cromwell, Conn., assignors to United Aircraft Corporation, East Hartford, Conn, a corporation of Delaware N0 Drawing. Filed Dec. 2, 1963, Ser. No. 327,552 5 Claims. (Cl. 75-174) This invention relates to columbium-base" alloys and methods of preparing them and has among its objects to provide a. group of alloys which are attractive for use from room temperature to M00 F. either as a structural member in the form of a rod, extrusion or large-size forging, or as tubing for conveying high temperature liquid metal; which are characterized by very high strength and creep resistance at 2400" R better than the best commercial columbium alloys available today; which have good fabricabi-lity, being capable of rolling to foil; and which possess corrosion resistance equal to that of electron beam produced Cb-lZr.

These and other objects and advantages .of the alloys of this invention will be evident from the following detailed description of a number of alloys and their properties which come the scope of the invention.

This :alloy family is intended for use up to 2400 R, which makes it very attractive for use in present nuclear reactors and it may well supplant the electron beam prepared Cb-lZr currently used for reactor applications. On a strength to weight basis, the alloys of this invention are superior to most tantalum and tungsten base alloys at 2400 F.

The alloys of this invention consist of columbium, zirconium and carbon in the following proportions:

This series of alloys have been prepared and subjected to intensive mechanical properties evaluation. The concentnations of the alloying agents were varied in the to lowing manners:

(a) The ratio of zirconium atoms to carbon atoms, at a fixed zirconium level, was varied to ascertain if any change in properties resulted from deviations from the atomic stoichiometry of one, i.e.,

Number of Zr atoms/number of C atoms-=1 (b) In order to vary the phase size and phase concentration of carbides, the total zirconium and carbon contents were increased from the 1 W/o level to the 5 W/O level, while maintaining a constant zirconium to carbon atomic ratio of 1.

On the basis of this work, it was determined that best strength results are obtained when the zirconium to carbon atomic ratio is maintained approximately equal to one. The greatest strength improvements were obtained by increasing the zirconium and carbon concentrations to the 3 w/o and 0.5 W/o levels, respectively; beyond this concentration level, any additional strengthening was considered fiairly marginal. The carbon additions were not found to be detrimental to the fabricability of worked material, whereas oxygen and nitrogen were detrimental to the ductility of even wrought Cb-Zr alloys. Furthermore, experimentation with a series of Cb-Zr alloys doped with oxygen and/or nitrogen revealed that little strengthening was produced at 2400 F., hence oxygen and nitrogen are considered undesirable constituents to the Cb-Zr-C alloy and every eiiort is exerted to reduce the level of these interstitials.

3,282,690 Patented Nov. 1, 1966 The preferred compositions for this family of alloys are:

The carbon levels are rigidly controlled to within of the desired composition in order to achieve reproducibility of properties. In addition, high purity columbium base metal is utilized to maintain low oxygen and nitrogen levels in the alloy.

Information about the properties and behavior of these alloys was [generated in the cfollowing areas:

1) Melting.Suitable alloys were prepared by nonconsumable and consumable are melting techniques, as Well as by employment of electron beam melting. Dense electrodes for melting were prepared by compaction of blended mixtures of powders, followed by sintering in vacuum at 2200 F. for two hours. Careful preparation of the alloy charge is extremely important for the following reasons:

(a) Due to a C0 boil in melting, carbon losses can be substantial; therefore, excess quantities of carbon, added as ObC, or Cb C, must be added to the charge to properly compensate for losses.

(b) In general, two carbides can be formed in the alloy and experimentation has indicated that the method of adding the carbon has an influence on th'e type of carbide formed as well as on the degee of alloying .and segregation. It has been our experience that carbon should be added as a carbide rather than as elemental carbon to achieve more rapid alloying with the metallic elements and a more uniform distribution. Generally the carbon is added as ZrC to whatever level of zirconium and carbon is desired, and excess carbon to counterbalance melting losses is added as CbC or Cb C. Excess concentrations vary from 5 to 25 w/o of the desired carbon level, depending upon the total carbon required and the melting technique utilized. Melting technique varies due to the fact that several are furnaces are available for melting and such operating factors as power, vacuum level, ingot size and molten pool size are different for e'achiurnace.

(2) Fabrication-These Cb-Zr-C alloys are completely fabricable under hot, warmand cold working conditions. The alloys were successfully extruded and/ or forged at temperatures from 2200 to 3300 F.; wrought forms such as rod, sheet, plate and tubing were successfully manufactured, as well as wire. In order to obtain optimum strengthening it is important to properly control Warm and hot working operations to achieve proper solutioning and precipitation for both fine particle strengthening and inter-action of dislocation networks with fine particles for additional strengthening. The effect of cold working on elevated temperature strengthening has also been determined.

(3) Heat Treatment.'Ihe heat treatment response of several of the alloys, Cb-l Zr-0.1 and Cb-3 Zr-0.3 C, has been thoroughly investigated with respect to stress relief annealing, recovery, recrystallization, grain growth and aging. This Work indicated cold worked material could be stress relief annealed by heating for l to 2 hours in vacuum at 2400 F. Also, recrystallization and grain growth occurred at 2900 F. or higher and generally was associated with the solutionizing of the carbide phase.

(4) Phase and Structure Studies.A study has been made of the carbide phases present in these alloys and the elfect of heat treating on their composition and structure of these carbides. Particular attention has been paid to the Cb-3 Zr O.3 C and Cb-l Zr-O.1 C alloys. Two

can be restored in part or almost fully by recrystallizing the material to .a fine grain size ASTM 7 .to 8 and concomitantly precipitating very fine carbides in the grain boundaries.

TABLE I.Cb-3 Zr-0.35 C Weld Data A. FUSION WELDED Test Configuration Weld Condition I Results As welded Heat treated 2 hrs. at 2,200 F Heat treated 2 hrs. at 2,200 F Heat treated 1 hr. at 2,400 F Heat treated 1 hr. at 2,400 F Specimen bent parallel to Weld Specimen bent parallel to weld Specimen bent perpendicular to weld- Specimen bent perpendicular to weld. Specimen bent parallel to weld Limited ductility, bent thru 11. Limited ductility, bent thru 32. Limited ductility, bent thru 29. Limited ductility, bent thru 51'. Complete ductility, bent thru 100 B. Cb-l Zr FILLER WELD Specimen bent parallel to weld As welded Limited ductility, bent thru Specimen bent perpendicular to weld. As welded Limited ductility, bent thru 15.

Specimen bent parallel to weld--- Heat treated 2 hrs. at 2,200 Complete ductility, bent thru 114.

Specimen bent perpendicular to we Heat treated 2 hrs. at 2,200 F Limited ductility, bent thru 22".

Specimen bent parallel to weld Heat treated 1 gr. at 2,400" F Complete ductility, bent thru 110.

Specimen bent perpendicular to weld Heat treated 1 hr. at 2,400" F Limited ductility, bent thru 29".

TABLE II TITLE: TENSILE STRENGTH DATA Test Yield Ultimate Percent Percent Alloy Temp. Strength Tensile Elonga- Reduction F. Strength tion in Area Cb-l Zr-0.1 C R.'I. 53,400 71,300 25 65 Cb-l Zr0.l C 2, 400 16,700 17,400 24 03 Cb-l Zr0 l C 2, 600 9,000 ,600 27 99 Clo-2 Zr-O 2 C 2, 200 23, 200 24,300 13 85 Cb-2 Zr-O 2 C--. 2, 400 15,600 16,400 15 81 Cb-3 Zr0.35 C .T. 89,600 122, 900 16 31 013-3 Zr-0 35 C- 2, 200 47,600 50, 700 8 64 (Db-3 Zr-O 35 C- 2, 400 22,500 23, 500 25 90 Cb-3 Zr0 35 C 2, 600 700 15, 300 27 96 Cb-3 Zr-O 4 C.-. .T. 63,600 80,500 19 32 Cb-3 Zr-O 4 O 2, 200 39, 700 ,800 14 96 Cb-3 Zr-0.4 C--. 2, 400 23, 500 24, 400 23 86 (lb-3 Zt-0.6 C 2, 400 14,200 16,000 18 70 Cb-4 Zr-O 7 C. 2, 200 26, 300 200 15 53 011-4 Zr0.7 C 2, 400 21, 200 25, 500 12 61 (lb-5 Zr-O 6 C 2,200 32,800 37,700 9 57 (lb-5 Zr-O.6 O 2,400 ,500 26,300 10 56 electron transmission metallography study has been made TABLE III of the grain structure and substructure of the Cb-3 Zr-0.3 C and Zb-1 Zr-0.1 C alloys. Particular attention has been paid to the dislocation characteristics of these alloys,

interactions in these alloys.

2200 F. in air.

temperature.

0.35 C and Cb-lZr-0.1 C alloys. in Table III.

TITLE: 100 HOUR STRESS TO RUPTURE DATA SUBTITLE: MATERIAL IN EXTRUDED CONDITION, TESTED IN VACUUM and a theory of strengthening has been proposed on the basis of dislocation-dislocation and precipitate-dislocation Alloy Test ggifj lfi Temp. 11 F. Rupture tion in Area (5) Oxidation Resistance.-The oxidation behavior of Llfe the Cb-3 Zr-0.3 C and Cb-l Zr-Oal C alloys was determined to be similar to that of CB-l Zr from 1600 to CM C 51388 31383 "as 2, 400 4,500 28 05 2,150 1 7,000 4 4 (6) Weldwbzlzty. These alloys can be successfully 2, 400 13,000 28 fusion welded or welded with filler wire, made from Cb-l ,gg 888 35 84 Zr or the base metal itself. Sheets from 45 up to 100 21150 71500 a "is mils thick have been successfully welded by both fusion 7 12,0) 27 84 and filler techniques. Welded alloy sheet material has been subjected to extensive bend testing, all tests conlTestsmppedmld complemn d t d according 1. h t d d f th M t i l Ad- It will thus be evident that as a result of this invention visory Board 4T test) and typical results for Cb-3 Zr-0.3 an improved col-umbium-base alloys have been Provided and C are summarized in Table I. In the as-welded coudian improved method of making them, enabling large tion, the alloy was not brittle but possessed limited ducstructural members and large-Size foreings to be tility; complete ductility was achieved by the appropriate stfucte'd which an p use from room p annealing treatments listed in Table I. ture to 2400" F. as Well as tubing for conveying high- (7) Strength.-The tensile strengths of the alloys were temperature liquid metal from a reactor core, for examdetermined as a function of fabrication history and test ple, to more remote parts of the reactorsylstem.

These results are summarized in Table II, It Will further be evident that as la. result of this inven- Creep rupture testing was concentrated on the Cb-3 Zrtion improved columbium-base alloys have been provided Results are presented having high strength and good creep resistance at 2400 The greatest trength values in the Cb-3 F. and Which have excellent fabricability and good cor- Zr-0.3 C alloy were delevoped by warm extruding at ros-i'on resistance at this elevated temperature. 3050 to 3150 F. The influence of annealing, cold Work- While our invention has been described by means of ing and recrystallization upon the strength of the Cb-l certain specific examples, it is to be understood that the Zr-0.1 C. and Cb-3 Zr-0.35 C has been delineated. In scope of the invention is not to be limited thereby except general, cold working causes a strength reduction which as defined by the following claims.

We claim:

1. An article of manufacture having good strength, creep resistance, corrosion resistance and fabricab-ility up to temperatures of about 2400 P. which consists essentially of, by weight, 18% zirconium, and 0.051% carbon, balance colurnbium having a low oxygen and nitrogen interstitial content.

2. An article of manufactuer according to claim 1 in which the oxygen and nitrogen interstitial contents are, by Weight, as follows, 0-150 p.p.m. oxygen and 0200 ppm. nitrogen.

3. A colu mbi-urn base alloy having high tensile strength and good creep resistance at 2400" P. which consists essentially of, by weight, about 1% zirconium and about 0.1% carbon, balance .columbium.

4. A columbium base alloy having high tensile strength and good creep resistance at 2400 P. which consists essentially of, by Weight, about 3% zirconium and about 0.35% carbon, balance columbium.

5. In the preparation of the colu-mbium-zirconiumcarbon alloys, the method of making the carbon addition to the alloy comprising the steps of, admixing high purity columbium and zirconium carbide in a Weight ratio of columbium to zirconium substantially equal to that desired in the cast alloy, adding excess carbon thereto in the-form of a second carbide selected from that group of carbides consisting of CbC and Cb C, the amount of carbon added in the second carbide equal-ling that lost in the melting process, and melting the mixture in a noncontaminating atmosphere.

References Cited by the Examiner DAVID L. RECK, Primary Examiner.

C. N. LOVELL, Assistant Examiner. 

1. AN ARTICLE OF MANUFACTURE HAVING GOOD STRENGTH, CREEP RESISTANCE, CORROSION RESISTANCE AND FABRICABILITY UPTO TEMPERATURES OF ABOUT 2400*F. WHICH CONSISTS ESSENTIALLY OF, BY WEIGHT, 1-8% ZIRCONIUM, AND 0.05-1% CARBON, BALANCE COLUMBIUM HAVING A LOW OXYGEN AND NITROGEN INTERSTITIAL CONTENT. 